1. Field of the Invention
This invention relates to a heat exchanger. More particularly, this invention relates to a heat exchanger provided with improved corrugated fins and intended mainly for use in automobiles.
2. Description of Prior Art
The heat exchangers (evaporators, condensers, heaters, etc.) in automotive air-conditioner systems and the heat exchangers such as automotive radiators preponderantly come in a fin-and-tube type having corrugated fins interposed one each between the adjacent folds of tubes, a laminate type having a multiplicity of tray-shaped plates laminating one over another so as to give rise to tubes for passage of coolant and having corrugated fins interposed one each between the adjacent tubes, and a serpentine type having corrugated fins interposed one each between the adjacent folds of a flat tube which has been extrusion molded so as to contain therein a multiplicity of holes for passage of coolant.
FIG. 1 is a cross sectional view illustrating a typical heat exchanger of the laminate type. This heat exchanger 1 has tray-shaped plates (pieces) 2 joined in pairs along their peripheral flanges 3 after the fashion of the shell of a cream puff to form therein a tube unit 5 incorporating a passage 4 for heat transfer medium 4, a plurality of such tube units 5 superposed one over another to give rise to empty spaces 6 therebetween, and corrugated fins 7 disposed one each in such empty spaces 6. The coolant which is introduced via an inlet side conduit 8, passed through the interiors of the tube units 5, and discharged via an outlet side conduit 9 exchanges heat with the air which is flowing along the fins 7.
A heat exchanger of the serpentine type is constructed as illustrated in FIG. 2. This evaporator 11 is formed by winding flat tubes 14 possessing a multiplicity of holes 13 for passage of heat transfer medium and disposing corrugated fins 15 one each in the empty spaces occurring between the adjacent folds of the tube 14. The heat transfer medium which is admitted via an inlet side conduit 16, passed through the interior of the tube 14, and discharged via an outlet side conduit 17 exchanges heat with the air which is flowing along the fins 15.
FIG. 3 is a perspective view illustrating part of the heat exchanger of FIG. 2 as magnified. A corrugated fin 15 is provided in each of the folds thereof with a louver 18 as illustrated in FIG. 3. In a similar corrugated fin used in other types of heat exchangers, a similar louver is formed in each of the folds. The formation of such louvers 18 in the corrugated fins 15 is intended to enhance the overall heat transfer coefficient of the corrugated fins by enabling the louvers to manifest an edge effect without necessitating any change in the overall surface area of the corrugated fins including louvers.
It will be observed that in each FIGS. 1, 2, and 3, the liquid tubes are arranged to have a plurality of flat, parallel radiating surfaces and that the corrugated fins have U-shaped bends juxtaposed to and in heat contact with these radiating surfaces.
The louver in each fold of the corrugated fin may be of the type having the blades thereof alternately projected from the base plane A of the fin and arranged parallelly to the base plane A as illustrated in FIG. 4, the type having the blades similarly projected from the base plane and slanted by a fixed angle relative to the flow of wind (indicated by the arrow) as illustrated in FIG. 5, or the type having a first half group of blades divergently slanted at a fixed angle and a last half group of blades convergently slanted at a fixed angle relative to the flow of wind as disclosed in U.S. Pat. No. 3,250,325, for example.
In the case of the louver of FIG. 4, however, if the interval d between the adjacent louver blades is small, the air flow boundary layer (indicated by dotted lines) for the first louver blade l.sub.1 grows so much as to cover completely the second louver blade l.sub.2 and lower the heat transfer coefficient of the second louver blade l.sub.2. The degree of the loss of heat transfer coefficient decreases in proportion as the interval d increases. When the width w of the louver blades is decreased for the purpose of enhancing the efficiency of the corrugated fin, the interval d mentioned above is inevitably decreased proportionally. As the result, the loss of heat transfer coefficient in the second and following louver blades is increasd possibly to a point where the improvement in the so-called louver effect can no longer be expected.
In contrast, the louver of FIG. 5 and the louver of the aformentioned U.S. patent have substantially no effect of the air boundary layer and prove advantageous in terms of heat transfer coeffieient. The flow of air entering these louvers, however, is bent by the louver blades in the directions indicated by the arrows while passing between the adjacent corrugated fins. In these louvers, the louver blades function as resisting objects to the flow of air. The heat exchanger using such corrugated fins as incorporating such louvers, therefore, offers large resistance to the flow of air and low heat exchange efficiency.
An object of this invention, therefore, is to provide an improved heat exchanger.
Another object of this invention is to provide a heat exchanger provided with corrugated fins which are free from the effect of air flow boundary layer and offers no appreciable resistance to the flow of air.